If you browse the Solr query service and get the following error, see the resolution below.
HTTP Error 404.3 - Not Found
The page you are requesting cannot be served because of the extension configuration. If the page is a script, add a handler. If the file should be downloaded, add a MIME map.
HTTP activation is likely missing from the server features. Enable http activation in both .Net 3.5 and 4.5.